As a power source, an outboard motor mounted to an engine (internal combustion engine) typically has a shift unit that performs control of connection/disconnection of rotational power output from the engine and switches a rotation direction and a water pump that feeds a coolant to the engine. In Patent Literature 1, there is discussed an outboard motor having a shift unit provided in the middle of a drive shaft extending straightly downward from the engine and a water pump provided over the shift unit. This water pump is mounted on the drive shaft and operates by virtue of the rotational power transmitted from the drive shaft. In this configuration, the water pump can be operated during the operation of the engine regardless of the shift position of the shift unit.
However, the configuration of Patent Literature 1 has the following problem. The water pump has a deformable impeller typically formed of an elastic material such as rubber and arranged inside a pump room. In addition, the impeller is rotated by the rotational power transmitted via a pump drive shaft. While the pump drive shaft is removed from the water pump, the impeller arranged inside the pump room is deviated (decentered) from an axial bore formed in the housing of the water pump. For this reason, in order to install the water pump to the housing of the outboard motor, it is necessary to assemble the water pump inside the housing of the outboard motor. Therefore, as described in Patent Literature 1, when the water pump is arranged in a far deep position inside the housing of the outboard motor, it is difficult to perform an assembly work or maintenance of the water pump.
A pilot shaft serving as a center of steering of the outboard motor is provided in front of the drive shaft of the outboard motor. For this reason, in the configuration of Patent Literature 1, in order to avoid interference between the water pump and the pilot shaft, it is necessary to increase a distance between the drive shaft and the pilot shaft or provide the pilot shaft over the water pump. However, if the distance between the drive shaft and the pilot shaft increases, a length from the pilot shaft to a center of the outboard motor also increases. For this reason, the moment of inertia in rotation of the pilot shaft of the outboard motor also increases, so that steering performance and gliding performance are degraded. In addition, if the pilot shaft is provided over the water pump, it is necessary to shorten the pilot shaft. For this reason, rigidity is degraded in a portion of the ship hull for supporting the outboard motor, and the steering performance is degraded.